TFT is a kind of transistor and is widely used in display field. The TFT in the prior art comprises a gate, a gate insulation layer, an active layer, a source, and a drain.
A display panel generally comprises an array substrate. The array substrate is provided with a plurality of pixels, each of which corresponds to one TFT. Each of the pixels is controlled by a corresponding TFT, so that an image can be displayed. The requirement for the performance of the TFT is increasingly high with the development of the display industry. In general, the TFT needs to have a relatively large saturation current. The saturation current of the TFT can be obtained through the following equation:
            I      ds        =                  1        2            ⁢              uC        OX            ⁢              W        L            ⁢                        (                                    V              gs                        -                          V              th                                )                2              ,wherein u represents a carrier mobility ratio of the active layer, COX represents a capacitance of per unit area of insulation layer, W represents a channel width of the TFT, L represents a channel length of the TFT, Vgs represents an electric potential difference between the gate and the source, and Vth represents a threshold voltage. It can be seen from the above equation that, u, W, and L are all main factors affecting the saturation current of the TFT. In the TFT, short circuit would easily occur to a source-drain metal layer if a value of L is too small. At the same time, an aperture ratio of the TFT would be reduced and a direct coupling capacitance between the source-drain and the gate would be increased if a value of W is too large. Therefore, increasing a value of u is one of the most effective methods for improving the saturation current of the TFT. In a word, a TFT with a relatively high carrier mobility ratio is urgently needed.